. >> pelley: it is a sunday of sorrow for newtown, connecticut, and for the nation. this afternoon hundreds of residents walked the road to sandy hook elementary school, where, on friday, 26 people were murdered, 20 of them children in the first grade. president obama has been in newtown tonight for a memorial service. first reports of this tragedy have turned out to be inaccurate. we were told that the gunman's mother was a teacher at the school, that he was allowed in because he was recognized, and that he targeted his mother's classroom with two handguns. tonight we know that all of that is wrong. here's what we do know, as told by people who knew the gunman and by one woman at the school that he approached but did not kill. that woman is sally cox, the school nurse. this picture was taken shortly after she left sandy hook elementary on friday. she's been the school nurse there 15 years. and she told us that friday morning began with comforting routine: 9:10, pledge of allegiance; 9:15, outside doors locked. then came 9:30. >> cox: all of a sudden, i heard a very